A clutch in an automobile contains frictional material on a SS or MS plate/sheet. A clutch disc moves to and fro, it is engaged while moving and while disengaged, it is stationary. The friction material used n clutches is very expensive and is attached to the SS plate mechanically with rivets. But these rivets prevent the entire material from wearing off (entire material should be worn off, if not, material wasted on plate adds to expense), wearing off occurring only up to the rivet head. Thus only 40% wears off, 60% is wasted. Further these clutches contain springs for smooth operation of clutch when gears are changed.
Various remedies have been attempted to improve the performance of clutch, including silicon based applications. One of them is oriented towards compositions that can be used as adhesives which are replacement to the rivets used.
In general, epoxy based material are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties. Epoxy adhesives are a major part of the class of adhesives called “structural adhesives” or “engineering adhesives”. These high-performance adhesives are used in the construction of aircraft, automobiles, bicycles, boats, golf clubs, skis, snowboards, and other applications where high strength bonds are required. Further, epoxy adhesives can be used as adhesives for wood, metal, glass, stone, and some plastics.
Two critical characteristics which determine the commercial use of adhesive is the shear strength and the peel strength. Standard epoxy resin compositions based on bisphenol-A and epichlorohydrin compounded with various thermally active latent hardener and optionally accelerators, fillers, thixotropic auxiliaries and the conventional additives are hard and brittle in the cured state. They exhibit very high tensile strength but on exposure to impact, peel stress, they flake leading to failure of the adhesive joints.
References may be made to U.S. Pat. No. 6,645,341 discloses a two-component epoxy-based adhesive comprising a resin component and a curing agent where the resin component comprises an epoxy resin, a polymer polyol, and fumed silica. The curing agent comprises a polyoxyalkyleneamine, an amine terminated butadiene-acrylonitrile polymer, tris(2,4,6-dimethlaminomethyl)phenol, polyamide resin, silane and fumed silica. Further, Table 1 of said patent describes adhesives with various additives consisting of resin and curing agent in a molar ratio of 3:1 and Table 2 mentions that the ingredients of the curing agent portion of the adhesive described in Table 1 affect the lap shear strength and peel strength of the adhesive. However, said patent does not disclose the measurement of the lap shear strength of the adhesive composition at elevated temperature. The adhesive composition is useful for bonding of metals, plastics and composites and for functions such as laminating, honeycomb bonding, automotive assembly and construction assembly.
References may be made to patent application US2011039108, relates to a heat-curable structural adhesive composition of high impact strength comprising one or more epoxy-resins of glycidyl ethers of bisphenol A, toughening agents, a curing agent capable of cross linking the epoxy resins and an acetoacetoxy-functionalized compounds.
Attempts have been made to toughen the epoxy resin based adhesives for low temperature applications. But adhesive compositions for clutch application have a requirement of high temperature stable epoxy resin composition coupled with a high lap shear strength i.e. bond strength while simultaneously balancing the required cushioning property.
Very few compositions balance both these requirements; however, there is a gap in the art which can be filled by providing an improved adhesive composition that delivers improved lap shear strength without a compromise on its cushioning property. Moreover, a need is felt to provide a clutch disc adhesive composition such that it is worn off completely, thus making it an economically friendly option to mechanical rivets, soldering techniques for bonding, which retains such improved properties at higher temperatures.